A light source generally emits light in every direction. For example, the light is emitted 360 degrees around in a hemispherical pattern. Said another way, the light source generally emits light in all directions.
However, certain applications require that light from the light source be directed in a certain direction or in a certain pattern. For example, light that is emitted in an uncontrolled manner wastes much of the light. For example, much of the light would not be used to illuminate a target area or illuminate the target area evenly if the target area is in a particular shape. Therefore, using a light source without any devices to control the direction of the light is undesirable.